1. Field of the Invention
This invention relates to a recording device to be used for copying machine, facsimile, word processor, printer for output of computer, etc., particularly to a recording head which performs recording by utilizing heat energy and a recording device having said recording head mounted thereon.
2. Related Background Art
First, description is made about the background art before the present inventors accomplished the present invention by referring to an ink jet recording head which can preferably practice the present invention as an example.
For example, as shown in U.S. Pat. No. 4,723,129 (Endo et al), there is an ink jet recording head suitable for performing a recording method to form an image by use of a recording liquid, which forms at least one droplet of a recording liquid (ink) by utilizing heat energy. The ink jet recording device having such recording head mounted thereon has been used as a printer 100 as shown in FIG. 1A. FIG. 1B shows the main constitution of recording head, etc. of the printer shown in FIG. 1A. Here, the ink jet recording head 401 receives the electrical signals from the driving circuit 408 and, while moving along the guide rail 402, attaches droplets on the recording paper 404 as the recording medium carried by the platen 403 and held at a predetermined recording position, thereby effecting recording of letters, graphics, etc. with dot pattern.
Here, 406 is an ink tank for housing the ink to be used for recording, which is detachably mounted on the ink jet recording device and supplies ink through the supplying tube 407 to the recording head 401.
Numeral 405 is a discharging recovery device, which is provided to bring the ink discharging state of the recording head 401 into good state before performing recording (see U.S. Pat. No. 4,600,931, Terasawa).
Next, the structure of the ink jet recording head of the prior art is described by use of FIGS. 2A and 2B.
FIG. 2A shows a heater 501 and a pair of electrodes 502 for forming an electricity-heat converting element as an energy generating means which generates energy to be utilized for discharging of ink. The electrodes 502, for receiving supply (transmission) of signals from outside, have the portion shown by 502a electrically connected to the driving circuit not shown by wire bonding, etc. The cross-section of the ink jet recording head cut along the line 2B--2B in FIG. 2A is shown in FIG. 2B.
The heater 501 and the electrodes 502 are constituted basically of a heat-generating resistance layer 501-1 formed through an intermediary insulating layer 503 on the substrate 505 and an electroconductive layer formed by patterning on said heat-generating resistance layer 501-1. The insulating layer 503 comprises an insulating material such as SiO.sub.2, SiN, etc. And, the insulating layer 503 is provided for the purpose of electrical insulation when the substrate 505 is formed of a material of a metal or semiconductor, etc. and additionally for the purpose of accumulating moderately the heat energy generated at the heater 501 and transmitting the heat with good efficiency into the liquid channel (nozzle) 506 filled with ink. However, for example, if the insulating layer 503 is too thick and accumulates too much heat, the temperature of the ink as a whole is elevated, whereby the physical property values of ink change and no stable droplet formation for obtaining good images can be effected. For this reason, the thickness of the heat accumulating layer may be suitably 2 to 5 .mu.m in the case of, for example, the material as described above.
Further, on the heater 501 and the electrodes 502, protective layers (504 and 507 in the drawing) are formed at their upper parts for the purpose of shielding these from ink. As the material constituting the protective layer, for example, inorganic materials such as SiO.sub.2, SiN, etc. may be employed for the first protective layer 504, and inorganic materials such as SiO.sub.2, SiN, etc. for the second protective layer 507. Also, in the vicinity of the heat-generating portion for generating bubbles to cause the ink to undergo change in state with heat, cavitation resistance layer 508 is formed for the purpose of preventing damage in the vicinity of the heat-generating portion by cavitation during shrinkage and disappearance of the bubbles generated. As the material constituting the cavitation resistance layer, for example, inorganic materials such as Ta, Ti, Cr, etc. may be employed.
In the prior art, for example, in a head having a structure described in U.S. Pat. No. 4,559,543 (Toganoh et al), since the supplying means of driving signals is provided separately from the substrate on which the electricity-heat converting element is formed, the head was electrically connected to the supplying means by wire bonding, etc. For this reason, when a large number of nozzles are arranged at high density, the area occupied by the signal connecting portions becomes larger than the area occupied by the nozzle portion, whereby not only the head is enlarged to bring about troubles in operability, but also the cost of material cost, etc. is increased.
Particularly, in a recording head in the form in which the ink tank for housing ink to be supplied to head is constituted integrally with head, and mounted detachably in the carriage of the ink jet recording device (see U.S. Pat. No. 4,635,080, Watanabe), since it is one of great factors for commercial success to produce a recording head at low cost and provide it at inexpensive price, the present inventors have investigated by carrying out a large number of experiments repeatedly in order to develop a recording head with a novel constitution.
Also, as one having a constitution different from the recording head with the constitution as disclosed U.S. Pat. No. 4,559,543 Togonoh et al as described above, there is a head in the form as described in U.S. Pat. No. 4,429,321 Matsumoto. This has been accomplished as the result of finding that the semiconductor related techniques can be applied to the head which performs recording by utilizing heat energy as described above, and a transistor as the driving element is made on the single crystal silicon substrate and an electricity-heat converting element is formed by thin film technique. However, in a head for high density and high resolution recording having as many as several tens to several hundreds of discharging orifices and electricity-heat converting elements as used in recent years, the number of individual electrodes of the respective electricity-heat converting elements is also increased, whereby it is difficult to effect miniaturization and reduced cost of the head.
Accordingly, it is required to have a constitution in which a plurality of electricity-heat converting elements is divided into, for example, M groups each of N elements to effect N.times.M matrix wiring, and current is passed selectively through the electricity-heat converting elements according to block driving such as time sharing driving. Such constitution is described by use of FIG. 3.
In FIG. 3, R.sub.11 -R.sub.MN are electricity-heat converting elements, C-1-C-M are common wirings of respective groups, S-1-S-N are common signal selection wirings, and by selecting respectively the group wiring and the common signal selection wiring and effecting conduction therebetween, driving of desired electricity-heat converting element can be done.
At this time, for breaking the circuits passing through other electricity-heat converting elements, to each of the group wiring is required to be connected a diode for prevention of reverse current at a part of the driving circuit.
Accordingly, the present inventors have progressed the investigations and consequently found that the recording head as described below is a suitable constitution.
That is, its constitution is that a diode array is made within the substrate on which electricity-heat converting elements are formed, by use of Si as the substrate material, and driving is effected by time sharing. As described above, by making diodes within the substrate, for example, for one having 64 electricity-heat converting elements, for which in the prior art one common electrode and 64 individual electrodes, namely at least 65 as the total of connection numbers and area therefor have been required, only 18 connection numbers and area therefor are required, whereby the number of steps necessary for connection and area can be lowered to accomplish miniaturization of the ink jet recording head.
Also, as accompanied with such miniaturization, the number of ink jet recording heads which can be prepared from one Si wafer is increased, and therefore cost-down to great extent can be also accomplished.
In addition by making the diode array within the head, the head size as a whole can be miniaturized, and not only the material cost of the head but also the cost of the surrounding circuit can be further lowered to great extent.
However, even in a recording head by matrix driving as described above, the wiring itself of the matrix circuit is complicated, and there is still room to be improved for effecting miniaturization and reduction in cost of head.
Particularly, in a recording head to be applied to the ink jet recording device as described above, it is difficult to obtain good images unless the influence of heat given to ink, propagation of vibration of ink accompanied with discharging, channel resistance, etc. are sufficiently taken into consideration.